1. Field of the Invention
The present invention relates generally to laboratory equipment and apparatus, and more specifically to an improved multiwell assay and/or culture strip.
2. Description of the Prior Art
Multiwell trays are typically made of molded plastic, such as polystyrene, and have a number of generally identical well portions arranged in a row and column array. Each well in the tray is analogous to a small test tube. Multiwell trays are generally intended as single-use disposable items. A popular type of multiwell tray is the microplate (also known as microtiter plates, micro-test plates, or simply, plates). A microplate is about the size of a postcard and about one-half inch thick, with ninety-six wells arranged in an array of eight rows by twelve columns. Microplates are widely used for growing (culturing) living cells and in performing a variety of research and diagnostic tests (assays) such as detection and identification of antibodies, viruses, bacteria, drugs or other substances. It is a common practice to treat or coat the wells of a microplate with biological substances such as antigens or antibodies for use in particular assays. Various steps routinely performed in the course of culturing cells or performing an assay can include inserting objects into the wells for mixing or sampling the contents, filling the wells with liquid, emptying the liquid from the wells, and photometric reading which consists of passing a beam of light through the well and its contents to be measured by a photosensitive detector.
As the use of microplates became more widespread, instruments were developed to perform and automate various steps of the culturing and assay procedure. An ad hoc standard configuration for microplate and well dimensions emerged as new manufacturers produced microplates or developed equipment intended to be compatible or competitive with those already in existence.
As many different types of assays were developed (and are still being developed), it became clear that, in many cases, the standard ninety-six-well microplate format represented an inconveniently large number of tests. To permit smaller numbers of tests to be performed conveniently, a number of manufacturers have produced modules or strips of wells corresponding to only one row or column of wells on a microplate. In keeping with the standard microplate configuration, these microwell strips generally contain either eight or twelve wells. All of the presently available microwell strips require the use of a rectangular retainer or frame member to hold the microwell strips. These frames have the same outside dimensions as the outer edge of a traditional microplate, and hold up to eight twelve-well strips or, alternatively, twelve eight-well strips. Therefore, a frame when completely filled with strips has the same dimensions and number of wells as a microplate.
The frame performs several functions. It holds the strips upright and facilitates handling since single strips usually tip over easily, spilling the well contents. The frame allows the user to assemble a microplate-sized unit with between one to eight rows or between one to twelve columns of wells. Since the frame itself matches the outer dimensions of a microplate, it allows the use of these microwell strips with certain microplate-compatible equipment. Each well in a strip is usually uniquely identified with a letter or number. Since the location of a particular well may be important in specific cultures or assays, each frame generally includes some visual or mechanical mechanism so that strips are uniformly aligned in the frame with their wells in the same sequence.
There are some inherent disadvantages associated with use of the frame. It is a component which is not directly involved in the culturing of cells or performance of the assay so its presence increases costs for production, packaging and handling. Use of a frame also increases the user's handling requirement since strips must be manually placed within the frame or removed from it to get the desired number of wells. Also, because the maximum capacity of any frame is ninety-six wells (eight twelve-well strips or twelve eight-well strips), multiple frames are required when more than ninety-six wells are desired. Also, although the strips are intended as single-use disposable items, the frame can represent a potential source of contamination if used more than once. This risk may predominantly occur in commercially available test kits or other packaging configurations where one frame is typically supplied with a full complement of strips.